The invention relates to a device for stabilizing the supply to a consumer, which during normal operation is supplied from an energy store from a buffer store. In particular, the device relates to stabilizing the supply to a consumer which is connected to a vehicle electrical system.
Stabilizing the supply of consumers, for example measurement instrumentation temporarily present in a vehicle, is effected by the provision of a buffer battery or a buffer capacitor as a buffer store. Due to the high capacity and the short-term achievability of high currents, both during energy withdrawal as well as charging, in most cases electrochemical capacitors in the form of so-called supercapacitors (also referred to as ultracap or supercap) are employed as a buffer store. By means of the buffer store is to be ensured that the consumer does not unexpectedly fail or exhibit undefined behavior during a drop in the voltage provided by the energy store below the minimum voltage needed by the consumer. The buffer store is usually dimensioned such that an even briefer operation of the consumer is made possible, so that this may bring itself into a defined state or be brought into a defined state. In this example directed towards motor vehicles, the energy store can be a vehicle battery, at the supply terminal of which the supplied voltage may fluctuate due to dynamic processes in the vehicle. In principle, however, this problem can occur in other applications. For the sake of simplicity, reference in this specification is made with respect an application in a vehicle, however this application is to be considered limiting.
In order to prevent that other components are also supplied by the buffer store during a drop below the necessary minimum voltage needed for the operation of the consumer, which would greatly reduce the time for stabilizing the supply of the consumer, a diode is provided between a node to which the consumer and the buffer supply are connected and the energy store or the other components. The presence of the diode entails that unwanted power dissipation (heat) is caused through the drop in voltage, which in principle should be avoided. Furthermore, the voltage swing that can be made available to the consumer via the buffer store is reduced by the voltage drop across the diode. Due to the necessary minimum voltage of the consumer, only a small operating range of the buffer store can therefore be used.
In order to provide the consumer a constantly high voltage independent of the voltage of the energy store, a DC-to-DC converter can be disposed between the aforementioned node and the energy store. In this way, the voltage provided by the energy store is (as a rule) transformed up (step-up), whereby the operating range of the buffer store can be increased. During operation, however, the DC-to-DC converter causes a constant power loss, which is given off as heat.
It is an object of the present invention to provide a structurally and/or functionally improved device for stabilizing the supply to a consumer, which during normal operation is supplied from an energy store, from a buffer store.
Proposed is a device for stabilizing the supply to a consumer, which during normal operation is supplied from an energy store, from a buffer store, which comprises a DC-to-DC converter, a plurality of controllable switching elements and a control unit for controlling the switching state of the plurality of controllable switching elements depending on an input voltage of the device.
The device is designed to supply the consumer during normal operation, while bypassing components having power losses, directly from the energy store when the input voltage is greater than a preset first limit voltage, wherein the first limit voltage is a minimum voltage of the consumer required for the supply of said consumer. This allows the consumer, if a stabilization of its supply is not necessary, to be operated with minimized losses in the voltage stabilizing device.
The device is further designed to supply the consumer via the DC-to-DC converter fed from the energy store when the input voltage sinks below the first preset limit voltage, wherein the DC-to-DC converter converts the input voltage into an operating voltage of the consumer. The DC-to-DC converter is activated only when the minimum voltage for the consumer can no longer be provided through the energy store. This is first fed from the energy store such that the buffer store for stabilizing the supply to the consumer need not yet be activated. This therefore makes it possible to push back temporally the activation of the buffer store.
The apparatus is further designed to feed the DC-to-DC converter from the buffer store when the input voltage sinks below a second preset limit voltage until a voltage of the buffer store reaches the second preset limit voltage, wherein the second preset limit voltage is a minimum voltage of the DC-to-DC converter for the operation thereof. The buffer store is thereby connected with the consumer by means of the device via the DC-to-DC converter. In this case, the connection is first made only when the voltage provided by the energy store is no longer high enough to operate the DC-to-DC converter.
The proposed device thus enables a later start of discharge of the buffer store, which allows a longer supply to the consumer. The buffer store can further be more deeply discharged in comparison with known solutions, which also enables a longer supply to the consumer. Due to the absence of a diode, the buffer store can additionally be charged to a higher voltage, which also brings an increased voltage swing and enables a yet longer supply to the consumer. Each measure creates individually as well as in combination a maximization of the buffer capacity of the buffer store.
As a result, the consumer operated with this device is optimally stabilized independent from fluctuations or failures of the energy store. There is no loss of power in normal operation. Furthermore, no critical consumer stress states may occur.
The device can comprise a controllable third switching element, via which the consumer can be connected directly to the energy store, whereby the consumer can be supplied during normal operation directly from the energy store, while bypassing components having power losses. The heat generated by the device is thereby minimal.
The device can comprise a fourth switching element which is interconnected between an output of the DC-to-DC converter and an output of the device, whereby the DC-to-DC converter can be connected to the consumer via the fourth switching element. If the fourth switching element is closed, the third switching element is then open, so that a direct connection between the consumer and the energy store is disconnected.
The device can comprise a controllable first switching element which is interconnected between an input of the DC-to-DC converter and an input of the device, wherein the DC-to-DC converter can be connected with the energy store via the first switching element, whereby the consumer can be supplied by means of the DC-to-DC converter fed by the energy store when the input voltage sinks below the first preset limit voltage.
The device can comprise a second switching element, which is interconnected between the input of the DC-to-DC converter and a connection to the buffer store, whereby the consumer can be supplied by means of the DC-to-DC converter fed by the buffer store when the input voltage sinks below the second preset limit voltage.
The device can be designed such that the first and the second switching elements do not have the same switching state in normal operation, wherein normal operation comprises all operating states with the exception of safety shut-off, in which all switching elements of the device are turned off. This means that if the first switching element is closed, the second switching element is open, and vice versa. This ensures that either only the energy store or the buffer store is connected to the input of the DC-to-DC converter. This can be ensured by means of appropriate control of the two switching elements or by means of a switch provided as hardware, so that the first and the second switching elements can only be displaced in the corresponding switching state with a control signal.
The device can include a controllable fifth switching element which is interconnected between the output of the DC-to-DC converter and the connection to the buffer store, whereby the buffer store can be charged. The fifth switching element can be closed at given intervals if the consumer is not supplied with power. The fifth switching element can be closed at given intervals if the consumer is not supplied with energy via the DC-to-DC converter, but rather directly from the energy store. The fifth switching element can be closed at given intervals if the consumer is supplied with power via the DC-to-DC converter. It is understood that when the buffer store is to be charged by the closing of the fifth switching element, the connection between the input of the DC-to-DC converter and the input of the device must also be closed, so that the DC-to-DC converter can be supplied with energy. In other words, this means that the first switching element must also be closed.
The control of the switching elements is performed by the control unit. This means that this must be supplied with voltage in order to perform this task. For this purpose, the control unit is supplied with voltage from the input of the device or from the buffer store. It is thus ensured that the control unit functions both on initial operation, when the buffer store is still empty, as well as until the end when the energy store and the buffer store are empty.
The control unit can be designed so as to detect the input voltage. The control unit can be designed so as to detect the output voltage of the DC-to-DC converter. The control unit can be designed so as to detect the voltage of the buffer store by measurement. Depending on at least one of these voltages, the control unit can be designed so as to determine the switching states (closed or open) of the switching elements, i.e. the first to the fifth switching element.
The buffer store can be an electrochemical capacitor, such as a supercapacitor or an ultracapacitor. These have a high energy density and the ability to quickly charge and discharge. The buffer store can be dimensioned such that it enables a supply to the consumer for about one minute after the start of discharge. In principle, the size of the buffer store is to be adapted respective to the application.
The buffer store can be a component of the device. The buffer memory can also be a component separate from the device.
The invention is explained in more detail in the drawings below with reference to an exemplary embodiment.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.